Multilayer wiring structures are used to increase the integration of semiconductor devices.
Although multilayer wiring structures are applied to increase the integration of semiconductor devices, it becomes easier for signals to transmit through internal insulation layers as the signal frequencies increase. Therefore, it is required to reduce the dielectric constants of the internal insulation layers for further increasing the operational speeds of semiconductor devices. In general, a SiO2 film (silicon dioxide film) is used, and the relative dielectric constant (written as the dielectric constant in the following) of SiO2 is 4.0 and as lesser dielectric constant material, a SiOF film with a dielectric constant of 3.6 is under investigation. Recently, a SiOCH film as a low dielectric material having a dielectric constant of 2.8-3.2 has become in practical use. Thus, a stream of research and development of internal insulation layers is developing technology based on silicon (Si) dominated material doped with fluorine or carbon.
For such requirement, a fluorine-doped carbon film (fluorocarbon film) is being investigated for application as a material with a low dielectric constant at less cost relative to conventional materials. The fluorine-doped carbon film can have its dielectric constant lowered to be about 1.8, and it is believed that the fluorine-doped carbon film is a promising film as an internal insulation layer that is applicable to high speed operation devices. On the other hand, the fluorine-doped carbon film includes carbon as the dominant element, and the characteristics of the fluorine-doped carbon film are quite different from those of a conventional film. For example, compared to a film that includes silicon as the dominant element, there are disadvantages of the fluorine-doped carbon film including less heat resistance, low mechanical strength, and low etching resistance to plasma etching processes.
Thereby, a multilayer structure formed with fluorine-doped carbon films applied for a semiconductor device and the fabrication method are different from those of the conventional film that consists of silicon as the dominant element. The following briefly describes a wiring pattern formation process, a dual damascene process using a fluorine-doped carbon film (F-doped carbon film) for applying an internal insulation layer.
FIG. 8(a) shows a process step in the middle of the process forming an upper circuit layer on a lower circuit layer 101 that is formed on a substrate 100. There are a F-doped carbon film 102, a copper (Cu) wiring layer 103, a capping film 104 made of such as SiCN (silicon carbon nitride), a barrier metal film 105, and a barrier film 106 for preventing the diffusion of the wiring material (Cu, in this case) into the F-doped carbon layer 102. On the lower circuit layer 101, a multilayer film is formed from the bottom to the top: a F-doped carbon film 112, a capping film 114, a metal film 117 made of such as Ti (titanium), a sacrificial film 118, and a photoresist mask 119. The F-doped carbon film 112 (102) is formed by exposing the substrate 100 to an atmosphere of plasma being generated from treatment gas that includes a C5F8 gas with a ring structure, such as carbon fluoride gas.
After forming the multilayer structure shown in FIG. 8(a), a formation process of a concave part 122 is performed for the F-doped carbon film 112 as shown in FIG. 8(b). This process includes forming the sacrificial film 118 using the photoresist mask 119, a viahole 120 for the F-doped carbon film 112 using the sacrificial film 118, and a trench 121 (trench for wiring material) in the F-doped carbon film 112 using a hard mask that is formed by patterning the metal film 117. Next, as shown in FIG. 8(c), a barrier metal film 115 is formed to cover the inside of the concave part 122 and the exposed surface of the wiring layer 103, followed by filling the concave part 122 with the wiring material, copper 113. Next, an excess of the copper 113 and the metal film 117 are removed by CMP (Chemical Mechanical Polishing), as shown in FIG. 8(d).
In the CMP process, to protect the F-doped carbon film 112 from the direct mechanical force, as shown in FIG. 8(d), the CMP process is stopped to retain part of the capping film 114. Further, an oxidized film 123 is formed on the surface of the wiring layer 113 by oxidization. If the oxidized film 123 is left on it, the resistance of the wiring layer 113 is increased. In order to deoxidize the oxidized film 123, as shown in FIG. 8(e), the substrate 100 is irradiated by plasma caused by excited ammonia (NH3) gas (named NH3 plasma). The F-doped carbon film 112 is etched if exposed to the NH3 plasma. However, as described above, the capping film 114 remains on the surface, so that the capping film 114 acts as a protecting film so that the NH3 plasma does not etch the F-doped carbon film 112 because the film 112 is not exposed. Following that, the barrier film 116 is formed over the entire substrate 100 including the surface of the wiring layer 113, and the forming process of the upper side circuit layer is completed (FIG. 8(f)). Further followed by succeeding similar processes, the multilayer structure of the semiconductor device is fabricated.
As described above, the capping film 114 acts as a protecting film of the F-doped carbon film 112 for the CMP process and the NF3 plasma irradiation, and furthermore it acts as an adhesive layer to stick the metal mask, the metal film 117 and the F-doped carbon film 112. Thus, as described below showing an experimental result of a comparative example 2-1, when a metal film made of Ti is directly formed on an F-doped carbon film obtained from a ring-structured C5F8 gas, the metal film 117 delaminates. Therefore, in terms of providing the intermediate capping film made of SiCN, SiC or SiN, the adhesion of the F-doped carbon film 112 and the metal film 117 is maintained.
Although the capping film 114 is not used for a conventional internal insulation film 112 of silicon related material, the F-doped carbon film 112 has been required recently because of the advantage of the low dielectric constant property. On the other hand, as the semiconductor device becomes thinner, the F-doped carbon film 112 as an internal insulation film is required to be thin. The materials of the capping film 114, SiCN (dielectric constant: about 5), SiC (dielectric constant: about 7), or SiN (dielectric constant: about 8) have relatively high dielectric constants. When the F-doped carbon film is used as part of the internal insulation film 112, the high dielectric constant of the capping film 114 becomes dominant when the internal insulation film 112 becomes thin. Namely, due to the high dielectric constant of the capping film 114, the effective dielectric constant of the internal insulation film 112 increases with decreasing film thickness, and even if the F-doped carbon film having a low dielectric constant of 1.8, is used, the advantage of the F-doped carbon film becomes less effective.
Further, the capping film 114 is used to compensate for the disadvantages of the F-doped carbon film regarding heat resistance and strength. But the capping film 114 is not essential for fabricating devices. Thereby, it may be regarded that the capping film 114 formation is an additional film formation process. Furthermore, the metal film 117 as a hard mask is necessary for the succeeding process, and it is required to choose an etching gas while maintaining a selectivity of etching rates for the metal film 117 as a hard mask. Further, in some cases, a cleaning treatment process may be required to remove the remaining substances generated while etching the capping film 114. Therefore, for a F-doped carbon film, in may be regarded that the number of process steps increases, which becomes a throughput reduction factor, and additional equipment may be necessary for performing the process.
On the other hand, one topic about a F-doped carbon film is described in a patent reference 1. However, there is no topic on the subject described above.
Patent Reference 1 Japanese Laid Open Patent Application 2005-302811.